The invention relates generally to a sensor for detecting skewed or disconnected adjacent movable components, and more particularly to a sensor for detecting skewed or disconnected aircraft control surfaces such as slats or flaps while ignoring relatively smaller harmless skews caused by normal flight.
Aircraft wings employ high-lift devices that are sometimes known as auxiliary airfoils or control surfaces. During takeoff and landing of the aircraft, the pilot can extend these control surfaces from a leading or a trailing edge of a wing to increase aerodynamic lift. When extended, the surfaces increase the effective size, curvature, camber, and area of the wing. This extension increases the lift of the wing for slow-speed flight. Control surfaces that extend from the leading edge of the wing are usually known as slats, while those that extend from the trailing edge of the wing are known as flaps. Slats are used primarily to increase lift at large angles of attack, while flaps are designed primarily to increase lift during landing.
An actuation system for the control surfaces converts electrical or hydraulic power, depending on the aircraft, into mechanical force that extends or retracts the control surfaces. Typically, a single lever in the cockpit controls both the slats and the flaps. In various aircraft designs, single or multiple actuators have driven a single control surface. Most frequently, multiple separate but coordinated actuators are used on each control surface, one or more on the inboard side, and one or more on the outboard side of the surface.
A control surface actuator is typically a geared device contained in the wing driven by hydraulics or by an electric motor. The actuator moves a rigid spar called a xe2x80x9ctrackxe2x80x9d that in turn extends or retracts the control surface. An actuation system may fail, for example, if the actuator gears strip, if the spar becomes disconnected from either the control surface or the actuator, or if the motive power (electric or hydraulic) is interrupted to the actuator. An actuation system problem is called xe2x80x9cdormantxe2x80x9d when it is not readily detected by inspection during ground maintenance, but fails later in flight. A dormant problem is a latent failure.
When two independent actuators drive a single control surface, only limited asymmetrical movement of the leading or trailing edge, respectively, of a slat or flap that is not parallel to the leading or trailing edge of the wing, respectively, will be tolerated. Such misaligned movement is called xe2x80x9cskew.xe2x80x9d If one of the actuators fails, skew of the surface that the actuator drives may occur. This skew may jam a control surface mechanism, thereby restricting control of the aircraft. A surface may jam if the forces on it are asymmetrical, just as a drawer in an ordinary dresser may jam if it is pulled on one side. In the worst case, if both actuators driving the same surface fail, the surface may separate from the wing and be lost.
A single actuator, supporting structure, and track may instead actuate a control surface. However, this method does not supply the desirable redundancy that multiple actuators afford. Multiple actuators, either of which will support the control surface, but not necessarily drive it alone, provide a margin of safety. Use of multiple actuators, however, requires synchronization, which requires additional complexity. In addition, the control surface must be structurally capable of withstanding the force of a failed single actuator while the remaining actuator or actuators apply force. With multiple actuators, weight must be still be kept at a minimum.
In one prior art method, a taut cable running the length of a wing detected skew of control surfaces. The cable sensed all control surfaces on the wing simultaneously when tension changes in the cable were measured. This method suffered from being relatively less sensitive to skew, and it was less capable of detecting which surface of several was skewed. Inductive proximity switches on control surface tracks have also been used for skew detection. The switches monitored track position and compared it with driveline position at the end of the wing. The proximity switch method suffered because the switches give an xe2x80x9conxe2x80x9d or xe2x80x9coffxe2x80x9d reading rather than a continuous output. For example, U.S. Pat. No. 5,686,907 to Bedell, et al. discloses a system that used both the cable and proximity switch methods. Such systems were in some cases not sensitive enough for regional jet applications.
Regional or business jets typically use low-profile, relatively small wings with smaller slats and flaps as compared with larger commercial aircraft that typically use larger, high-profile wings. Manufacturing and assembly tolerances, thermal conditions, wing dynamics, and backlash on the slats together result in stringent requirements on a sensing system. That is, a small xe2x80x98windowxe2x80x99 exists where sensing must take place. The sensor cannot be so sensitive as to create a false detection due to assembly tolerances, temperature, wing dynamics, and backlash that cause a relatively small amount of harmless skew. On the other hand, it must detect relatively larger amount of harmful skew on surfaces.
Accordingly, it is an object of this invention to provide a sensor that will detect harmful skew in any configuration having adjacent movable components.
Another object is to provide a sensor that will detect a failed aircraft control surface actuator or a broken connection between an actuator and the surface it operates.
It is a further object to detect an actuation system failure that may cause harmful skew or separation of an aircraft control surface from a wing while ignoring the relatively smaller harmless skew caused by assembly tolerances, temperature, wing dynamics, and backlash.
Another object is to provide a sensor that will detect harmful skew of a control surface and activate a circuit to warn the crew.
Still another object is to provide a sensor that will detect a lost control surface and activate a circuit to warn the crew.
Yet another object is to provide a sensor that is capable of de-energizing an actuation system to reduce aircraft damage after the sensor detects harmful skew or loss of a control surface.
Another object is to provide a sensor whose state can be determined by visible inspection during maintenance.
A further object is to provide a sensor that is repairable, re-settable, accurate, and reliable.
An additional object is to provide a sensor that will resist salt, insects, dirt, and other contaminants in an aircraft environment.
A major step in the invention is the recognition that a constraining means such as a mechanical fuse that separates at a predetermined tension, combined with a switching means, may be used to detect harmful skew of two adjacent movable components that exceeds a predetermined limit, while ignoring relatively small harmless motions.
According to the invention, a sensor that detects relative motion of two adjacent movable components comprises a base; a first arm pivotally connected to the base; a second arm pivotally connected to the base; a switching means integral with the first and second arms for detecting the position of the two arms with respect to each other; separating means for applying a force between the first and second arms; and means for simultaneously constraining the first and second arms in a closed position and the switching means in a closed position until a relative motion between the two adjacent movable components exceeds a predetermined limit, thereby causing a force on the first or second arm to exceed a predetermined limit, which causes the constraining means to release the arms from the closed position and also causes the separating means to apply a force to the first and second arms to move the first and second arms to an open position and to move the switching means to an open position.
In further accord with an aspect of the present invention, the switching means is operative to provide an indication that the first and second arms are in the closed or opened position, wherein the indication may be visual or may comprise a signal of an electrical, optical or some other nature that may be used by subsequent circuitry.
The invention has several benefits compared with prior art systems such as U.S. Pat. No. 5,686,907 to Bedell, et al. The present invention is more sensitive to the motion of adjacent movable components, in particular control surfaces, and it is better able to detect dormant problems before they become failures. In addition, the invention better protects against a false annunciation to the crew of a harmful control surface skew. It is also lighter than the prior art. The sensor of the present invention is re-settable by replacing or re-setting the means for constraining the arms. Finally, after an actuation of the sensor, it is simple to establish during ground maintenance where a failure occurred since there is physical evidence of a broken fuse or other means for constraining the arms.